What is Parkinson's Disease?

Parkinson's disease (PD) is a neurodegenerative brain disorder that progresses slowly in most people. Most people's symptoms take years to develop, and they live for years with the disease.

In short, a person's brain slowly stops producing a neurotransmitter called dopamine. With less and less dopamine, a person has less and less ability to regulate their movements, body and emotions.

Parkinson's disease itself is not fatal. However, complications from the disease are serious; the Center for Disease Control rated complications from PD as the 14th top cause of death in the United States.

Normally, there are brain cells (neurons) in the human brain that produce dopamine. These neurons concentrate in a particular area of the brain, called the substantia nigra. Dopamine is a chemical that relays messages between the substantia nigra and other parts of the brain to control movements of the human body. Dopamine helps humans to have smooth, coordinated muscle movements. When approximately 60 to 80% of the dopamine-producing cells are damaged, and do not produce enough dopamine, the motor symptoms of Parkinson's disease appear. This process of impairment of brain cells is called neurodegeneration.

The current theory (so-called Braak's hypothesis) is that the earliest signs of Parkinson's are found in the enteric nervous system, the medulla and in particular, the olfactory bulb, which controls your sense of smell. Under this theory, Parkinson's only progresses to the substantia nigra and cortex over the years. This theory is increasingly borne out by evidence that non-motor symptoms, such as a loss of sense of smell, hyposmia, sleep disorders and constipation may precede the motor features of the disease by several years. For this reason, researchers are increasingly focused on these "non-motor" symptoms to both detect PD as early as possible and to look for ways to stop its progression.

Medical content reviewed by: Nina Browner, MD—Medical Director of the NPF Center of Excellence at the University of North Carolina at Chapel Hill in North Carolina and by Fernando Pagan, MD—Medical Director of the NPF Center of Excellence at Georgetown University Hospital in Washington, D.C.